Transmission-line.



s.. i mfp JmL@ E. E. I', CRBIGHTON. TBANSMIBSION LINE. unicum: rmznsnm'. 11.11312.

Patented Mar.9,1915.

Fly?. 3 3

limi/enter: Elmerlff Creighton STATES PATENT OFFICE.

ELMEB E. F. CREIGHTON, OF SCHENECTADY, NEW YORK, ASSIGNOB. TO GENERALELECTRIC. COMPANY, A CORPORATION OF NEW YORK.

i Transmission-LINE. I

Patented Mar. 9, 1915.

V y 4iippiiaaaea iiiea sepiemberinisia. scrinium-11u14.

To dll whom it may concern.'

Be it known that I, Emmi p Ton, a citizen of the United States, residingat Schenectady, county of Schenectady, State of New York,havelinventedcertain new and useful Improvements in Transmis-'sion-Lines, of which the following is a specification.

My invention relates to systems of electrical distribution and moreparticularly to transmission lines which extend for many miles and aresubjected to varying influences, such as thunder storms and similardisturbancesl which tend to produce on the transmission line abnormalvoltages, surges and similar destructive phenomena commonlyincludedunder the term lightning.

Most of the surges, oscillations and simi lar disturbances which appearup'on transmission lines appear to be the result of inductive actionrather than of direct lightning strokes.- There are various causes forthese. disturbances, but in ve many cases the presence of a storm clouin the vicinity of a transmission line' will set up destructive surgesand oscillations on the transmission relation to only a comparativelysmall extent of the transmission line, but the inductive disturbance dueto 'the presence of the cloud quickly builds up into destructive surgesand oscillations, owin to the ease with which-surges and oscillationscan travel on the ordinary transmission' line. There also appears to bea tendcnc for lightning discharges in the vicinity o the line to in duceupon a considerable portion of the line a very high momentary voltagewhich is then distributed along the line with comparatively little lossand appears throughout the whole length of the line in the form ofsurges and oscillations which are destructi vc at tlicirlirstappearancc,orclse are built up by re cated inductive efi'ects from thocloud until they' become destructive. These oscillations and surges aretransmitted along the line ander favorable conditions, as thel ordinarytransmission line oflers very little damping cflIoct toelectrical.vibrations. 'lts impedance is distributed either uniformly orelse in the form of substantially equal impedance laced at ref'ularintervals alon r tho line.. t will vibrate electrically witii but slightdamping, in much the same way that a stretched string, either unloadedor E. F. Camion unifoimly loaded, will transmit vibrations with but Iittle loss or damping.

One object of my'invention is to revent on a transmission' system thedeve o ment o f oscillations and similar abnorma conditions by theinductive effect of a highly charged cloud or of a stroke of lightningin thevicinity of the transmission line. To a'ccomplish this result 1construct the line in 'such a. manner that oscillating and transitrydisturbances, iftransmitted along the line at all, are quickly dampedout. The line is made of a character unfavorable to the transmission ofsuch disturbances, and damps them out in much the same way as anirregularly loaded stretched'string danips out vibrations in it. lTosecure the desired effect, I make the conductors of the transmission'system electrically irregular by varying the impedance of the conductorin an irregular manner. Hi li frequency potential waves can travel a ongsuch a cou ductor only with the greatest .diiliculty, and standing wavescannot be added to the potential wave to produce destructive voltagepeaks. The conductor may be made elecline. Usually such a cloud is ininductive size. When the destructive surges and oscillations approach avalue freut enough to cause discharges to groan a discliarge orflashover may occur at almost any of the in` siilators. After such abreakdown or flashover, the entire line must be inspected in order todetermine at which insulator the ashover to ground occurred. Thisextended ins ection requires much time and is objcctiona le. lf thcdestructive efl'cct of' the surges and oscillations cannot be en tirelyeliminated, it is desirable that the discharges and flashovers-to groundshalltako place at selected insulators along the line, so that thedischarges shall occur at known points on the line, and another objectof my invention is-to cause the lashovers and discharges to ground totake place at certain selected insulators. To this end, I placeinipedancc near selected points to cause an abnormal voltagein theconductor to discharge at selected insulators rather than over theothers. In this way the other insulators are protected and thedischarges or flashovers occur at definite and known places wheredevices may be used to prevent actual damage.

A further object of my 4invention is to provide an improved formof.inductance `or 1o impedance device which is of simple and`rugged.construetion and can easily be inserted in series with thcconductors of a transmission system.

My invention will best be understood in connection with the accompanyingdrawing which merely for purposes of illustration shows diagrammaticallysome of the forms in which my invention may be embodied and in which-Figure 1 shows semi-diagrammatically an improved form of inductance,particularly suitable for being connected in series with the conductorof a transmission-line; Fig. 2 is a diagram showing a transmission'lmewith inductances distributed at irregular intervals along the conductor;Fig. 3 is a diagram showing another form of transmission line embodying`my invention; Fig. 4 is a diagramshowing the effect of. a conductorembodying my invention upon a surge or oscillation appearing upontheconductor; and Fig. 5 is a view 1n perspective of a polyphasetransmission line embodying my invention.

sa My invention may be embodied in various forms of transmission lines,one form being diagrammatically shown in Fig. 2, in which the conductor1 of the transmission line is provided at irregular intervals withconcen- 40 trated'inductances 2 connected in series with the conductor.By placing these induetances atirregular intervals, I break u theconductor-'into adjoining sections whic are electrically dissimilar sothat the conditions are made as unfavorable as possible for thedevelopment of stationary waves and for the transmission of surges andoscillations.

Even though the section or length of theconductor in which theoscillation first appears should be favorable to the development andtransmission of the oscillation,

the next section would not be and as a result the oscillation or surgewould quickly be damped out. The varying lengths and difteringelectrical characteristics of the ad- ]oining sections of the conductorrender the developmentof high frequency harmonics practicallyimpossible.

.Substantially the same result-ma.)1 be obo0 tained .1n the manner shownin Fig. 3, in

wh1ch lnductances 3 are distributed at uniform distances apart along theconductor,

but each mclutance differs in amount from each ad acent mductance. Theelectrical effeet 1s t e saine as in the form shown in Fig.

2 and as each section of the line difl'ers in impedance and otherelectrical characteristics from the adjoining, section, oscillations andsurges cannot travel for any distance alon the conductor. '.10

lVhile do not wish to advance any theory of operation the etl'ect whichis probably produced is shown diagrammatically in F ig. 4, in which thedotted line 4 shows a wave of potential set up hy an inductive '75discharge in the vicinity of th'e conductor. As this wave of potentialtravels along the conductor and encounters one of theindnctances 2 or 3it is broken up to some extent and reduced in amplitude and as it passes30 into the next section where conditions are unfavorable for itsamplitude, being increased by resonance it is again broken up andreduced by the action of the next induc-4 tauce and so onwith theresultthat oscillations and surges arel quickly damped out and kept belowdestructive values. Some idea of the value of these impedances duringthe formation of a lightning stroke may oo gained by the followingtheoretical explanationz-Before the quantity of electricity in the cloudgathers to one central point and breaks-through the atmosphere in a boltto earth, the charges on thc line are distributed along the line on thesections formed by'the 96 choke coils. As the lightning charge in thecloud gathers at one point, the corresponding induced charges on theline`follow the movement of the charges in the cloud and also gather atone point. If the line conx93 sists, as it generally does. of a straightwire the charge can be moved at practically the' Speed of light, thatis, 180,000 miles per second. These induced charges on the line willrush together from different directions and will pile up as one highpeak. With the presence of a' choke coil, however, the elcctrostatiecharge located between choke coils will be greatly retarded in itsmovement b v the time constant of the choke' coil. 113 The object is tomake these time constants greater than the time constantsof the dischare from the cloud so that the discharge will ave taken place and reversedbefore the charge in the lline can follow it. This will 'keep the charge'in the line more distributed and broken up into smaller parts and thusprevent the tremendous accumulation at one oint on` the line. It, asshown in Figal, t e supporting material between the terminals is roperlychosen with-a high resistance, consi erable part of the energy in thelocalized charges on the line may be absorbed by the fact that theysuddenly endeavor to pass through the choke coii.

The impedanees which I prefer to insert in the conductors of thetransmission line are preferably made in the form of inductance coilshavin some resistance in shunt. These coils I pre er to construct in theman rv;

tributed along said conductor to render ner shown in Fig. 1. Each end ofthe coil 2 is secured to a metal terminal 5 which is connected to theconductor 1. The terminals 5 are rigidly secured to the ends of a member6 w ich has a certain amount of resistance, and is in shunt to the coil2. 'The' member 6is preferably constructed to withstand the tensilestress exerted upon it by theegonductor. 'As aresult of thisconstruction the coil 2 is rigidlyA secured at the ends to the metalterminals 5, while the longitu dinal stress exerted by the conductor istaken up by tne member 6, which not only forms this figure one of theimpedances is placed close to a selected insulator 7 where in case theconditions are such that the charges cannot be held back as the mainstroke takes place (see previoutheoretical description) the flash overor discharge to ground will occur at this particular point. Under such`conditions, the presence of the inductance immediately adjacent theselected insulator produces a tendency to Hush over at the selectedinsulator in preference to the other insulators, and consequently theflash over or dischar e to ground is much more apt to occur'at t eselected insulator than at the others.

My invention may be embodied in many other forms than the recisearrangement disclosed and I, there ore, do not wish to limit myinvention to the precise arrangement disclosed except in so far as it islimited by the scope of the appended-claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A transmission line comprising a conductor having impedanceirregularly disi ua and adjacent lengths of said conductor e ectricallydissimilar and the whole conductor electrically irregular.

2. A transmission line comprising a conductor having impedanceunsymmetrieally distributedl along said vconductor at comparnativelygreatV intervals to render eve section of said conductor electrically dierent from an adjoining section of equal length and said conductorelectrically irregular throuhout its length.

3. transmission line comprising a conductor, and impedanceunsymmetrically distributed at comparatively great intervals along saidconductor to cause said conductor to be irregularly loaded withimpedance.'

4. A transmission line comprising a conductor, and impedances equal inamount distributed along said conductor at markedly unequal distancesfrom one another.

5. A transmission line comprising a conductor, and impedances equal 1namount and distributed along said conductor so that the distance betweeneach im edance and the next on one side differs y a substantial amountfrom the distance between said impedance and the next cn the other side.

6. An impedance device for insertion in the conductor of a transmissionsystem comprising a poorly-conducting member having suilicient tensilestrength to withstand the tensile stress exerted by the conductor andprovided with a metal terminal at each end, an inductance coilencircling said member with its ends secured to said terminals. andmeans counectin said terminals in series relation with sai conductor.

7. An impedance device for the conductor of a transmission systemcomprising an inductance coil shunted by a poorly conducting'core ofsuflicient tensile strength to withstand the pull of the conductor, amet-al terminal secured to each end of said core and of said coil, andmeans connecting said terminals in series relation with said conductor.

8. A transmission line comprisin a conductor and inductance coils shunteby resistance distributed'along said conductor to cause the impedance ofsaid conductor to vary irregularly.

9. A transmission line comprising a conductor, and impedance devices ofequal value distributed along said conductor at unequal intervals, eachof said devices comprising an inductance shunted b resistance.

In witness whereof, have hereunto set my hand this 9th day of September1912.

ELMER E. F. CREIGHTON.

